The present invention relates to a method of beneficiation for recovering copper and zinc concentrates separately from complex sulfide ores containing sulfides of copper, zinc, iron and other minerals.
The beneficiation of complex sulfide ores containing copper, zinc, iron and other minerals is generally done by a differential flotation method consisting of two principal steps: in the first step, the copper minerals are floated and sphalerite, pyrite and gangue are depressed with slaked lime, sodium cyanide and zinc sulfate to form a sink; in the second stage, copper sulfate or any other suitable activator is added to the sink so as to obtain an activated sphalerite froth while the pyrite and gangue are depressed to be separated as a sink. However, if the complex sulfide ores have undergone oxidation or other secondary geological reactions in the ore deposit, the respective minerals are so close in their response to flotation that considerable difficulty is encountered in their beneficiation by the conventional differential flotation method.
Japanese Patent Publication No. 15310/1962 proposed the use of sulfur dioxide gas in combination with sodium sulfide and zinc sulfate for the purpose of depressing sphalerite in the complex sulfide ores that had undergone secondary geological reactions, and this method produced some improvement in the results of beneficiation. However, the depression of the sphalerite requires the use of various reagents in high volumes, and the effectiveness of this method depends on using these reagents in the right amounts. The operation of this method therefore requires a high-degree control technology in order to implement a complicated process with a reliable reagent feed apparatus.
Magnetic separation of copper minerals by a strong magnetic field was proposed in Japanese Patent Publication No. 20694/1974. However, this method is unable to produce a copper concentrate of an industrially feasible high grade if the feed contains great amounts of pyrite and other paramagnetic minerals having comparable values of magnetic susceptibility.
The complex sulfide ores taken from mine A in Canada consist of chalcopyrite, bornite, sphalerite, pyrite and gangue. The ores have the following composition (wt%):
______________________________________ Cu Zn Pb S Fe SiO.sub.2 Al.sub.2 O.sub.3 CaO MgO ______________________________________ 1.67 2.31 0.06 31.26 27.21 12.8 3.75 1.78 3.85 ______________________________________
Analysis by EPMA (Electron Probe Microanalyzer) showed that the iron value in the sphalerite was 0.2-1.0 wt%. Having being subjected to oxidation in the ore deposits, these sulfide ores defined selective depression of the sphalerite by slaked lime, sodium cyanide and zinc sulfate in accordance with the conventional differential flotation technique. An attempt was made to enrich and recover the copper minerals from these ores by enhanced magnetic separation in accordance with the method shown in Japanese Patent Publication No. 20694/1974; first, the strongly magnetic materials were removed by a conventional magnetic separator with a field strength of 1,000 Gauss; then, the remainder was passed through an iso-dyanamic separator with a field strength of 15,000 Gauss. The results are shown in Table 1 below; the weakly magnetic materials had low copper values and copper concentrates of sufficiently high grade to be used industrially could not be obtained.
TABLE 1 ______________________________________ Weight Assays (%) Recovery (%) Product % Cu Zn Cu Zn ______________________________________ Mill feed 100.00 1.67 2.22 100.00 100.00 Strong magnetics 0.45 0.32 1.42 0.09 0.29 Weak magnetics 18.90 6.35 0.56 71.89 4.77 Nonmags 80.65 0.58 2.61 28.02 94.94 ______________________________________
As shown above, the recovery of copper minerals and sphalerite from complex sulfide ores conventionally requires the use of many reagents in large amounts and can only be realized through complicated procedures using high-degree process control technology.